Abstract: Some Lower Cretaceous Stratigraphic Models from Texas and Mexico

T. A. Bay, Jr.

Carbonate-ramp and carbonate-shelf depositional models are utilized in interpreting Lower Cretaceous carbonate stratigraphy in the Gulf of Mexico province. The lower Glen Rose (upper Trinity) high-energy, rudist reef and grainstone complex began on a low-relief carbonate ramp and prograded seaward over slightly deeper water, low-energy, calcareous mudstones and wackestones with a resultant growth of about 1,250 ft (380 m) vertically over a horizontal distance of 30 mi (48 km). During upper Glen Rose, Fredericksburg, and Washita deposition this same high-energy facies complex built about 1,300 ft (396 m) vertically in a horizontal distance of 6 mi (9.6 km), creating a marked break in slope between the shallow water of the shelf and shelf margin and the adjacent deeper wate of the ancestral Gulf of Mexico. This topographic break in slope changed the profile of deposition from a carbonate ramp to a carbonate shelf. A faster rising sea level, perhaps a result of more rapid rate of seafloor spreading, probably accounts for the pronounced vertical buildup.

Regional cross sections of Fredericksburg and Washita strata show the shallow-water depositional attributes of carbonate rocks on the Central Texas platform. High-energy grainstone and rudist-reef complexes separate the shallow-water carbonate rocks and evaporites from deeper water strata in the East Texas basin. During Washita deposition, deeper water also was present in the McKnight basin.

Sufficient density and acoustic contrasts are present within the prograding lower Glen Rose strata, which were deposited on a ramp profile, and the upper Glen Rose, Fredericksburg, and Washita strata deposited at the shelf margin, to recognize the character of these buildups on reflection-seismic profiles.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas